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Old 09-30-2017, 11:56 AM   #11 (permalink)
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For engine braking it doesn't matter if you are above the torque curve. Just select a low enough gear to achieve DFCO. Means you have to use it a lot later in the slow down cycle, but that doesn't mean you have to lose the benefit entirely.
I had an incident today, when I changed into 3rd at 50 mph, to slow for traffic building up ahead. Recorded about 4,000 rpm.

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Old 09-30-2017, 01:36 PM   #12 (permalink)
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Thanks for the feedback. Learned that today. Seeing the benefit of "dfco" when the vehicle speed is above 50ish km/h. Anything below that and I'm getting better numbers with the gearbox disengaged. From what I'm seeing on the app this car very rarely if ever shuts the injectors completely off. But my fuel numbers do drop "dfco" vs neutral coasting even with an indicated higher engine rpm so the injectors do throttle back. Fairly confident the app is working properly as i am seeing 0 liters consumed per 100k when using eoc. Still learning what is happening as I put time into the app. Need to stop beating myself up as I am getting pretty good mileage from this vehicle
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Old 09-30-2017, 02:22 PM   #13 (permalink)
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Another consideration: how is the app determining you're in DFCO? An OBD-II device doesn't have access to actual fuel injection metrics. So it's inferring DFCO either from user-settable throttle position + RPM settings or possibly from open/closed loop status, or a combination of both.

(On my car, it shows open loop in DFCO mode.)
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Old 09-30-2017, 02:23 PM   #14 (permalink)
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I miss my Saturn. Been so long since I rolled it I don't even remember what model it was. I broke 40 mpg most of the time with it and I was naught but a wee kid then(19). Drove it like I stole it most of the time. 38-42 is typically where I would end up.
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Old 09-30-2017, 03:52 PM   #15 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
Another consideration: how is the app determining you're in DFCO? An OBD-II device doesn't have access to actual fuel injection metrics. So it's inferring DFCO either from user-settable throttle position + RPM settings or possibly from open/closed loop status, or a combination of both.
I am gauging this by fuel flow readings, which never drop to 0/lph unless I kill the engine. Another question is if the app is measuring pump flow or actual delivery to (at) the injectors. So my previous assumptions, on dfco vs neutral coast may be wrong..

When this car is in neutral coast it holds the idle at ECU commanded 1100 rpm +- to help rev matching??. Where as when i am asking for dfco it's running off my input via throttle position sensor.. I do see the difference on fuel consumption in these two scenarios..

Neutral idle won't drop down to 750rpm until ECU detects 0 speed from the VSS..

I'll grab some screen shots and try some data logging a little later.. Going to pick up my sister and I have a looong 5km + downhill coast with a 70km/h limit

Good discussion, I appreciate it, I'm enjoying this little challenge!
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Old 09-30-2017, 03:56 PM   #16 (permalink)
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Quote:
Originally Posted by gpfaster View Post
Where as when i am asking for dfco it's running off my input via throttle position sensor.
DFCO only comes into force with no throttle input. You have to have your foot away from the accelerator.
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Old 09-30-2017, 04:17 PM   #17 (permalink)
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DFCO only comes into force with no throttle input. You have to have your foot away from the accelerator.

Yep doing that Going to do some driving with a multimeter hooked up. That'll tell me if (or under what conditions) the injectors are being told to shut down.. I hypothesize that this car won't do a true fuel cut off and that I should be trusting what the data is telling me..
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Old 09-30-2017, 04:22 PM   #18 (permalink)
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Looking forward to seeing your results. DFCO gives me great mileage figures.
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Old 10-01-2017, 08:22 AM   #19 (permalink)
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Quote:
Originally Posted by gpfaster View Post
Another question is if the app is measuring pump flow or actual delivery to (at) the injectors.
If you're using an OBD-II plug-in device, it's reading neither.

OBD-II computers estimate fuel consumption from air consumption , so fuel use is a calculation based the stoichiometric air/fuel ratio, engine displacement, RPM, MAP/MAF, open/closed loop status etc.).

So it may not actually know exactly when you're in DFCO. On the ScanGauge, for example, one of the parameters for detecting DFCO is user-settable (throttle position, maybe?).

I find my SG doesn't always report DFCO, or reports it much later than I know it's already happening. On the MPGuino on the other hand, DFCO shows up instantly (because it's directly monitoring fuel injector pulses).
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Old 10-01-2017, 08:47 AM   #20 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
If you're using an OBD-II plug-in device, it's reading neither.

OBD-II computers estimate fuel consumption from air consumption , so fuel use is a calculation based the stoichiometric air/fuel ratio, engine displacement, RPM, MAP/MAF, open/closed loop status etc.).
Thank you. That makes sense. I'm going to wire in a multimeter to the injectors to try and get some better info for myself then.. I have a feeling that at some point I'll be trying the scan gauge and mpguino route as well, enjoying the data and observations of what the car is doing..

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